1. Field of the Invention
The present invention relates to a wireless headphone system, and more particularly to an infrared signal emitting apparatus for emitting an infrared signal and wireless headphone apparatus for outputting an audio sound in response to the infrared signal. The infrared signal emitting apparatus and the wireless headphone apparatus are to be used in a vehicle or in the open air.
2. Description of the Related Art
Up until now, there have been provided a wide variety of wireless headphone systems comprising an audio apparatus and a wireless headphone apparatus, which can be used in, for example, a vehicle for the purpose that a passenger sitting in a rear seat can listen to a radio or a CD without disturbing the driver or passengers sitting in front seats.
One typical example of the conventional wireless headphone system is shown in FIG. 6 as comprising an audio apparatus 70 and a conventional wireless headphone apparatus 80. The audio apparatus 70 comprises a signal emitting unit 71 for emitting an infrared signal. The conventional wireless headphone apparatus 80 comprises an infrared signal receiving unit 81 for receiving the infrared signal transmitted from the signal emitting unit 71 of the audio apparatus 70 to output an audio signal. As shown in FIG. 6, the infrared signal receiving unit 81 receives extraneous light in addition to the infrared signal emitted from the signal emitting unit 71. This means that the audio signal outputted by the infrared signal receiving unit 81 contains a noise component caused by the extraneous light. The conventional wireless headphone apparatus 80 further comprises a noise filtering circuit 82 for eliminating the noise component caused by the extraneous light to output a filtered audio signal, an amplifier 83 for amplifying the filtered audio signal to output an amplified audio signal, and a speaker 84 for outputting a sound in response to the amplified audio signal.
The conventional wireless headphone system thus constructed as previously mentioned, however, encounters a drawback that the conventional wireless headphone apparatus 80 tends to receive sunlight, for example, coming through a window of the vehicle. The noise component caused by the sunlight cannot be eliminated by the noise filtering circuit 82 because of the fact that the sunlight includes strong infrared radiation. This results in the fact that the noise filtering circuit 82 outputs an audio signal with noise component caused by the sunlight and the speaker 84 outputs a sound with large noises.
In the vehicle, a passenger sitting in a left seat tends to receive sunlight from a left window, while a passenger sitting in a right seat tends to receive sunlight from a right window. This means that the infrared signal receiving unit 81 placed on the left side receives an infrared signal with less extraneous light while the infrared signal receiving unit 81 placed on the right side receives an infrared signal with sunlight in the case that the passenger sits in the right seat. The infrared signal receiving unit 81 placed on the right side, on the other hand, receives an infrared signal with less extraneous light while the infrared signal receiving unit 81 placed on the left side receives an infrared signal with sunlight in the case that the passenger sits in the left seat. This leads to the fact that the that the infrared signal receiving unit 81 placed on one side tends to receive an infrared signal with sunlight although the infrared signal receiving unit 81 placed on the other side may receive an infrared signal with less extraneous light.